Production of sheet material



March 19, 1963 H. o. HJELT PRODUCTION OF SHEET MATERIAL 3 Sheets-Sheet 1 Filed Sept. 5, 1958 \lu m0 H March 19, 1963 H. o. HJELT PRODUCTION OF SHEET MATERIAL Filed Sept. 5, 1958 5 Sheets-Sheet 2 March 19, 1963 H. o. HJELT 3,032,133

PRODUCTION OF SHEET MATERIAL Filed Sept. 5, 1958 5 Sheets-Sheet 3 United States Patent PRODUCTION OF SHEET MATERIAL Heikki Olavi Hjelt, Lindeman Naur, Ved Bellahoj 11st, Copenhagen, Denmark Filed Sept. 5, 1958, Ser. No. 759,349 Claims priority, application Great Britain Sept. 10, 1957 14 Claims. (Cl. 156-33) This invention relates to the production of sheet material.

The invention consists of a method of producing a sheet material comprising forming a series of layers consisting of fibrous material in a binding medium, each layer being formed by the steps of coating a forming surface with the binding medium, setting up an electrostatic field between the forming surface and a feed apparatus for'the fibrous material whereby the fibrous material is transferred to the forming surface, and flattening the fibres of the fibrous material, the formation of at least some of the layers comprising the further step of generally aligning the fibres before or during flattening, the fibres of successive layers being aligned in different directions, the material being subsequently removed from the forming surface.

Preferably the aligning is carried out immediately in advance of the flattening, conveniently by a transverse air stream.

The invention still further consists of apparatus for carrying out the method set forth in the preceding two paragraphs comprising an endless belt acting as forming surface and adapted to move past a series of layer-forming units each consisting of means for applying a layer of binding medium, feed apparatus for-fibrous material, means for setting up the electrostatic field'between the feed apparatus and the belt and means for flattening the fibres of the'fibrous material, at least some of the layer-forming units further comprising means for generally aligning the fibres situated in advance of the flattening means, the aligning means of successive units being arranged to align the fibresin different directions, means also being providedto remove the material so produced from the belt.

The invention still further consists of sheet material manufactured by the method according to the invention.

The invention will be further described with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic elevation illustrating a single stage of the plant for carrying out the invention,

FIGURE 2 shows a modified multi-stage apparatus,

FIGURE 3 showsv a detail of the apparatus of FIG- URE 2,

FIGURE 4 is a diagrammatic side elevation of a further multi-stage apparatus according to the invention, and

FIGURE 5 is a perspective view, partly in section, of a detail of FIGURE 4,

FIGURE 6 shows in elevation, partially broken away, part of a modified form of feeder unit, 7

FIGURE 7 shows in plan a detail of FIGURE 6, and

FIGURE 8 shows' the arrangements for transferring cellulose to the feeder unit.

Referring particularly to FIGURE 1, reference numeral 1 indicates a container holding binding material. A transfer cylinder 2 carries the binding material from the container 1 onto the surfaceof the roller 3. When the roller 3 during its revolving movement in the direction of the arrow A has turned through 45 the part of its surface, which has been coated with the binding material, arrives opposite the container 4,.holding fine fibrous material. There is created an electrostatic tension between the cylinder 4 and the fibrous material, which causes the fibres to be ejected with considerable force against the coated surface of the roller. If e.g., a voltage of 40,000 v. (3 ma.) is used, there will be created upon the surface of the cylinder a tissue 5 of some strength, composed of the binding material and fibres, which the doctor blade 6 detaches from the roller surface. Before the tissue layer 5 reaches the knife 6 it is compressed by roller 7, which strengthens the texture of the tissue, at the same time giving it very smooth surface.

The effect of the compressing roller can be accentuated by suitably heating the same.

After having been detached from the cylinder 3, by the knife 6, the tissue 5 falls upon an endless transporting belt 8. When travelling further on this belt the tissue 5 is sprayed by the nozzle 9 with chemicals, colouring or something like that, which are proper to strengthening its physical properties and/or appearance.

While travelling on the transporting belt 8 the tissue 5 passes between a pair of rollers 10. These are heated and the tissue dries while passing through them. If one pair of rollers do not give the desired effect, several pairs of them and infrared heat can be applied. These rollers not only dry the material, but also compress and smooth it.

Through the rollers 10 the material passes onto a second endless transporting belt 11, which carries the material through the finishing installation 12. Here the material received, e.g., a glazed surface, can be printed in figures and can be ultimately dried. The material leaving the finishing installation is either wound in rolls or cut into sheets.

When the fine fibres in the electrostatic field precipitate onto the surface coated with binding material, an amazingly even layer, of a velvet like appearance, is created. As even the finest filaments of the fibres open and spread out, owing to that peculiar effect of static electricity, the tissue created in this way results of an unsuspected strength, so that even paper and cardboard can be manu factured of dry cellulose fibres. If, e.g., condensed or polymerised artificial resin is used as binding material, a sheet of good physical strength, with a pleasant velvet like surface, can be produced. In such a case the condensing or polymerising catalyst can be sprayed upon the tissue by the nozzle 9 and the final condensing or polymerising can be effected between the rollers 10 or in the finishing phase 12. A great variety of different binding materials and glues can be used, in order to produce the desired efiect and quality.

Referring now to FIGURES 2 and 3 there is shown a multi-stage form of apparatus for carrying out the invention in which the roller 3 is replaced by an endless belt 13, driven by a roller 14, and being coated from transfer cylinder 2 with binding agent from container 1. The belt 13 is then driven past a feed point 15 for fibrous material and under a roller 16, placed obliquely across the belt 13 and driven in the direction indicated by the arrow. The roller 16 flattens the fibres in one direction and the flattened fibres are then sprayed with a further coating of binding agent from the nozzle 17. Then follows a further feed point 15a for fibrous material, and a roller 16a to flatten the fibres along a different direction from that of roller 16. The stages may be repeated to obtain a sheet of any desired thickness.

The belt 13 is subsequently fed between heated compression rollers 18 and then under a bank 19 of infrared lamps heating the sheet formed on the belt 13. The formed sheet 5 is removed from the belt in the region of dn'ven roller 14 by a doctor blade 6 as in FIGURE 1 and the sheet 5 subjected to a similar set of finishing operations.

The belt 13 is preferably formed of aluminium sheet strengthened laterally with metal-bars.

In either case the voltage employed for setting up the electrostatic field may be from l0l00 kv. with a maximum-current of about 3 ma, supplied by a transformer 20, the output of which is rectified and connected between the frame 21 of the apparatus and the fibre feed points 15.

FIGURE 3 shows a form of fibre feed point comprising a hopper 22 for fibrous material which opens to a reciprocable sieve 23 feeding onto a belt 24 which runs over rollers 25 rotating as indicated by the arrows and so maintained at ahigh potential. The belt 24 carries the fibres to a region beneath belt 13 where the electrostatic field takes elfect and carries the fibres onto belt 13' as shown.

Alternatively the fibrous material may be blown onto belt 24.

Referring now to FIGURE 4, an endless metallic belt 101 passes over a series of rollers 102, 103, 104, 105 supported on a frame 106.

The belt leaving the roller 105 is cleaned by a water spray 107 and rotating brushes 108 and subsequently dried by a heater indicated at 109.

The belt 101 is then given a coating of a greasy adhesive, e.g., petroleum jelly or the like, from a reservoir 110, the adhesive being fed by a roller system 111. After passing over roller 102 the belt 101 is passed .under a pneumatic and electrostatic feeder 112 for fibrous material and a light roller 113 to flatten the fibres. A spray 114 then' adds a coating of adhesive, e.g., 9%

aqueous polyvinyl acetate, and the feeding, rolling and spraying are repeated several times by further similar devices-112, 113 and 114 (not shown).

The sheet material formed on the belt 101 is then robust enough to stand further treatment and after leaving, for example, the fifth feeding device, indicated as 112a, it is subjected to a series of transversely directed air jets from adevice 116, to be described in more detail-with reference to FIGURE 5. These air jets have the effect of substantially aligning the fibres deposited on the belt by feed device 112a in a direction transversely of the belt and they are rolled into this position by the succeeding roller 113. Since the sheet material now has a greater thickness it is necessary to introduce a measure of interstage drying, e.g., by a stream of hot air from jets 1-17.

The belt then passes under a heavier roller 118 and the whole process of spraying, feeding, aligning, rolling, drying and further rolling is then repeated until this sheet material on the belt is of the requisite thickness.

At this stage the sheet material is passed over the heated rollers 103, 104 and 105, which may be maintained at progressively higher temperatures, e.g., 100 C., 130 C. and 160 C. respectively, and removed from the belt 101 by doctor blade 119 and/or air blade 120. The sheet material is then subjected to such finishing processes as may be desired, e.g., glazing, dyeing, and pressure treatment and final drying.

The process is continuous and may comprise some 12 to 16 stages in all, but for thicker materials or even 40 stages may be used.

The feeding devices 112 draw fibres, e.g., cellulose, from a reservoir by means of an air stream set up by fans 121. The fibres are passed down the tube 122 through successively finer screens 123, 124 and 125 located behind the fans and the tube 122 then opens out to form a chamber 126 of which the end wall is formed by a grid formed of a square metallic mesh located say 1- inch above the belt 101 and extending the full width thereof. A baffle 127 is provided to expand the air stream and may be pierced at 128 to prevent the formation of a central dead spot. Generally tangential air jets 130 are also provided to assist in this respect.

The screens 123, 124 and are slidably and sealingly mounted in the tube 122 so that they may be withdrawn, e.g., for cleaning, and may be extended so that replacement takes place simultaneously. Thus also a variation in the mesh size may be obtained. Similarly the end wall may be replaced and varied and it is traversed by a reciprocating rake, indicated diagrammatically at 129, to keep it continuously clear and avoid clogging of the mesh and caking of the "fibres.

The electrostatic fieldis applied between the end wall grid of the feeders 112 and the belt 101 by a high tension source 131 and-is-of the order of, e.g., 30 kv. for for a spacing of say 1 inch.

The forced feeding imparted by feeding device 112 enables the machine to be run at higher speeds than would be possible with purely electrostatic and gravity feeding, e.g., 2 yards per second.

The device 116 comprises an internal tube,-slotted at the bottom and connected to a source of pressurised air. Over this tube is slidably fitted the outer sleeve 132 which is illustrated more in detail in FIGURE 5. The sleeve 132 is formed with rows of slits 133, each slit in a particular row being equal but variations both of number and size of slots being possible asbetween the rows. The slits 133 are inclined at about 45 to the axis of the sleeve and thus when aparticular row of slits 133 is aligned'with the slot in the internal tube a series of transverse jets is applied to the fibres on the surface. Variation of the row byrotation of the sleeve 132 enables variation-of the strength and number of the I jets andthus imparts a degree'of control over the process.

The successive feeding devices 112, or groups of such devices, may, if desired, be utilized to feed different fibres and thus produce a composite sheet material. Also-the belt 101 may be kept just warm (e.g., 30C.) to facilitate thorough drying of the sheet material formed. In addi tion suitable arrangementofthe slits 13am the sleeve 132 can be made to cause a herringbone effect in the layer of fibres. 3'

In FIGURES 6 to 8 there is shown a modified method of aligning the fibres. These parts ofthe apparatus are designed to replace the corresponding parts in the pre viously described embodiment. FIGURE 6 shows a metal plate 201 with transparent, insulating shields 202, e.g., of perspex, dependent from the lateral edges thereof towards the belt 203. Secured to plate 201, either fixedly or adjustably, are a plurality ofpointed metallic conductors 204' (see also FIGURE 7). The fibres are fed into the belt from a feed apparatus 205, shown in some detail in FIGURE 8, andan air jet 206 is placed to inject air between the feed apparatus 205 and the plate 201.

With a belt of some 40 inches width the conductors 204 will be some four in number, although this figure is not limitative upon the invention in any way.

FIGURE 8 shows a hopper 207 for cellulose chips which are conveyed to a disintegrator 208 via a screw feed 209 and a conduit 211; The disintegrator may take any suitable form for reducing the raw material to individual fibres, e.g., a hammer mill or a form of carding apparatus. From the disintegrator 208 the fibres are-fed down a chute 212 to a shoe 213 overlying the belt 203.

The chute and shoe may be partly formed of transparent and insulating material, e.g., perspex, and'partly of metal which may then be brought to ahigh potential with the plate 201 to exercise some'infiuence onthe movement of the fibres. To increasc the speed ofthe fibres an additional stream of air maybe used in the chute. The transparent portions of the chute andshoe, as well as the shields 202 are made so in order to facilitate observation and hence control of the movement of the fibres. The shields 202 are provided to prevent escape of the fibres and for protection from lateral draughts which would upset the evenness ofthe fibre distribution on the belt 203.

The pointed conductors 294 each set up a jet of ionized air and the combined effect of the set illustrated will be to align the fibres at an inclination with the longitudinal axis of the belt and thus the conductors 204 replace the device 116.

By providing a second set of oppositely inclined con ductors 204 and means for alternately energizing them a herringbone effect may be obtained.

The interstage drying may also be carried out by infrared heaters or any other convenient method.

The belt may be of metal sheet or netting, or plastic textile or glass fibre material coated with a conductive metal layer.

In addition to fibre like or other similar homogenous materials, which are obedient in an electrostatic field, such as animal hair, straw, sawdust, or the like, also e.g., scaly minerals, colour pigments, filler materials, e.g., China clay, or the like can thus be advantageously used. Alternatively they maybe brought through the chute by an additional air stream or otherwise.

The process covered by this invention can be applied in the production of many kinds of sheet-like material, such as paper, cardboard, wall-paper, blotting and filtering paper, insulating and building board, roofing felt, parchment and materials similar to artificial leather, as at will the material produced by this method can also be created upon ready made textile or other material or only strengthened inside by such.

The process may be carried out by detaching the sheet formed'from the belt as soon as it is strong enough to be self-supporting, and thereafter passing it through a number of further feeding points with electrostatic fields between stationary members so that the material constitutes its own forming surface.

Various modifications may be made within the scope of the invention.

I claim:

1. In a method of forming a sheet material comprising superposed layers each consisting of fibrous material held together by a binding medium, the steps of forming a first layer by coating a forming surface with the binding medium, setting up an electrostatic field between the forming surface and feed apparatus for the fibrous material whereby the fibrous material is transferred to the forming surface, and flattening the fibres of the are formed in groups, successive groups of layers being formed of differing fibres, each group consisting of at least one layer.

8. A method of producing a sheet material comprising the steps of: laying down a first series of superposed layers on a carrier, each formed by deposit-ion of fibrous material onto binding medium placed on the previously formed layer on the carrier and flattening the fibres into the binding medium; laying down a second series of superposed layers on the first series, each layer of said second series being formed by deposition of fibrous material onto binding medium placed on the previously formed layer, aligning the fibres of the layer being formed and flattening the fibres in substantial alignment, the superposed fibres of successive layers of said second series being aligned in different directions; and removing the material so formed from the carrier.

9. A method as claimed in claim 8, in which the deposition of the fibres is carried out electrostatically.

10. A method of producing a sheet material comprising a series of superposed layers consist-ing of fibrous material held together by a binding medium, comprising the steps of, forming a first of said layers by coating a temporary carrier with binding medium, setting up an electrostatic field between the carrier and a feed apparatusfor the fibrous material, whereby the fibrous material is transferred to the carrier, and flattening the fibres of the fibrous material to form the layer; individually forming subsequent layers by coating the preceding layer with binding medium, electrostatically feeding fibrous material onto the preceding layer and flattening the fibres of the fibrous material to form the layer; the fibres of a plurality of the said subsequent layers being flattened into aligned posifibrous material into the binding medium; forming sec- 0nd and subsequent layers upon the preceding layer by coating the said preceding layer with binding medium, setting up an electrostatic field to transfer fibrous material from feed apparatus to the said preceding layer and flattening the fibres of the fibrous material into the binding medium, the fibres of a plurality of the layers being flattened into position, in which they are aligned in predetermined direction, the fibres of successive layers of the plurality having the flattened and aligned fibres being aligned in different directions; and removing the material from the forming surface.

2. A method as claimed in claim 1, in which a quantity of China clay as a filler is introduced with the fibrous material forming at least some of the layers and blown onto the forming surface therewith.

3. A method as claimed in claim 1 in which the aligned fibres in a layer are all aligned in the same direction.

4. A method as claimed in claim 1 in which the aligned fibres in a layer are aligned in a herringbone formation.

5. A method as claimed in claim 1 in which the aligning is carried out immediately in advance of the flattening.

6. A method as claimed in claim 5 in which the aligning is carried out by generally transverse air stream.

7. A method as claimed in claim 1 in which the layers tions, the fibres of successive layers of the plurality having the flattened and aligned fibers being aligned in different directions, the sheet material being removed from the carrier after formation of some of the subsequent layers but before completion of formation of all the layers.

11. Apparatus for producing a sheet material comprising a series of layer forming units, an endless belt acting as a forming surface and adapted to move past the series of the layer-forming units, each layer forming unit con- .sisting of means for applying a layer of binding medium,

feed apparatus for fibrous material, means for setting up an electrostatic field between the feed apparatus and the belt and means for flattening the fibres of the fibrous material, at least some of the layer-forming units further comprising means for generally aligning the fibres of the layer, such means being situated in advance of the flattening means, the aligning means of successive units being aranged to align the fibres in different directions, and means to remove the material so produced from the belt.

12. Apparatus as claimed in claim 11 in which the aligning means comprises a series of air jets located immediately in advance of the flattening means.

13. Apparatus as claimed in claim 11 in which the aligning means comprises a series of pointed conductors each arranged to be brought to a high potential to set up a generally transverse stream of ionized air.

14. Apparatus as claimed in claim 13 comprising two series of pointed conductors are provided to give oppositely inclined streams of air and means for alternately energiz ing the two series of conductors whereby a herringbone alignment is achieved.

References Cited in the file of this patent UNITED STATES- PATENTS 2,407,548 

1. IN A METHOD OF FORMING A SHEET MATERIAL COMPRISING SUPERPOSED LAYERS EACH CONSISTING OF FIBROUS MATERIAL HELD TOGETHER BY A BINDING MEDIUM, THE STEPS OF FORMING A FIRST LAYER BY COATING A FORMING SURFACE WITH THE BINDING MEDIUM, SETTING UP AN ELECTROSTATIC FIELD BETWEEN THE FORMING SURFACE AND FEED APPARATUS FOR THE FIBROUS MATERIAL WHEREBY THE FIBROUS MATERIAL IS TRANSFERRED TO THE FORMING SURFACE, AND FLATTENING THE FIBERS OF THE FIBROUS MATERIAL INTO THE BINDING MEDIUM; FORMING SECOND AND SUBSEQUENT LAYERS UPON THE PRECEDING LAYER BY COATING THE SAID PRECEDING LAYER WITH BINDING MEDIUM, SETTING UP A ELECTROSTATIC FIELD TO TRANSFER FIBROUS MATERIAL FROM FEED APPARATUS TO THE SAID PRECEDING LAYER AND FLATTENING THE FIBERS OF THE FIBROUS MATERIAL INTO THE BINDING MEDIUM, THE FIBRES OF A PLURALITY OF THE LAYERS BEING FLATTENED INTO POSITION, IN WHICH THEY ARE ALIGNED IN PREDETERMINED DIRECTION, THE FIBRES OF SUCCESSIVE LAYERS OF THE PLURALITY HAVING THE FLATTENED AND ALIGNED FIBERS BEING ALIGNED IN DIFFERENT DIRECTIONS; AND REMOVING THE MATERIAL FROM THE FORMING SURFACE. 